Trench tractor



Aug. 4, 1931.

G. H. GREIMAN TRENCH TRACTOR Filed Sept. 6, 1928 7 Sheets-Sheet 1 Geo/396 fl 6116 Aug. 4, 1931. G. H. GREIMAN TRENCH TRACTOR Filed Sept. 6, 1928 '7 Sheets-Sheet 2 George g- 4, 1931- G. H. GREIMAN 1,817,367

TRENCH TRACTOR Filed Sept. 6} 1928 7 Sheets-Sheet 3 Aug. 4, 1931. v G. H. GREIIMAN 1,317,357

TRENCH TRACTOR Filed Sept. 6. 1928 7 Sheets-Sheet '4 $Iyj2 fl6reiinan y .4463

Aug; 4, 1931. G. H. GREIMAN 1,817,367

mama TRACTOR Filed Sept. 6, 1928 '1 Sheets-Sheet 5 a 2 5: m IIHIII"In".llllllllllllnllll 'I'IIIIIIIIIIH" "lull IMP Jib.

J2 42 42 A 42 H 7 Aug. 4, 1931. G. H. GREIMAN 1,817,367

)TRENCH TRACTOR Filed Sept. 6. 1928 7 Sheets-Sheet 6 5 7 5 5 3 3 0 9 0 a 2 0 0 9 .w w/ m s iv! I .........W W. .anminwznmi Aug. 4, 1931. G. H. GREIMAN 1,817,367

TRENCH TRACTOR Filed Sept. 6, 19 28 '7 Sheets-Sheet 7 fllllwlllTllllllliiim Patented Aug. 4, 1931 t imSm-ES GEORGE H. Gasman, oia 'eann'nit. IOWA TRENCI-I ritlidron Application filed September 6,19f28fSeria1No. 304,287.

My present invention has for its object the provision of a self-propelledtrench tract-or I Fig. 7 fragnientary'detail view in secadapted to travel in a trench and follow a trenching or excavating machine to act as sheathing to holdup the walls of the trench as it is dug by said machine, and inwhich trench is to be laid sewer, water, gas or other pipes or conduits.

In the preferred form of the trench trac tor, it is designedto draw thereafter asheathing device to hold up the walls'of a trench back of the tractor where theworkmen are. laying a'pipe or pipe sections in the trench;

to prevent the walls of the trench from caving in on the workmen and their work.

To the above end,i generally stated, the invent-ion consists of the novel devices and combinations I of devices hereinafter de scribed and defined in the claims.

In the accompanying drawings, which illustrate the invention, like characters indicate like parts throughout the several views.

Referringtothe drawings; Fig. 1 is a view diagrammatically illustrating a trenching machine in the process '1 of digging a trench and further illustrating I I I parti'y. in section taken substantially on the the trench tractor following the trenching machine in the trench and drawing a sheath- 1 with the exception that'the trenching ma- I I 1 Fig. 1I6.isa perspective view of the sheathchine is removed and the trench tractor, and

sheathing device are shown moved partwayout of the trench, and further illustrating matically illustrating the trench tractor and sheathing device as the same are transported I showing the trench in transverse vertical secfrom place to place;

Fig. 41 is a front end elevation of the parts.

shown in Fig. 8; I V

further illustrating supplemental sheathing extensions on the trench tractor. and sheath ing-device to hold the walls of the trench l at their increased depth;

Fig. 6 is a View principally in transverse F 8 isa fragmentary view principally in i: 3 Fig. 12 is a' view and partly in transverse vertical section takenon the irregular line 12,'12 of Fig. 8; Fig.1? is a fragmentary detail view principally inplan, but withsome parts broken -;a.Way and sectioned, illustrating the pawl and ratchetdriving, mechanism for the wall I 1 i Fig. '19 is vertical section taken on the line 6-6 of Fig. .5;

tion takenon the line. 7-7 of Fig. 5, on an enlarged scale;

side elevation of the trench tractor and 1 sheathing device, on an'enlarged scale;

"Fig 9 is aview partly in end elevation and par ly in transverse vertical section taken on the rre'gularline 9'9 of'Fig. 8;

Fig. 10 is a view principally in plan of the I parts'showii in Fig. :8, and with some parts sectionedron the line10..-l0 of Fig. 8;:

OFFICE,

F llii's a view partly in plan partly 5 in horizontal section taken on the line 1 111 of-Fig.8; i

partly in end elevation retaining traction belts c 'F1g.i1'4 is a viewpartly in end elevation and line 14+14of Fig. 8;

: 1 Fig. v15.is a view partly in elevationand "Epartly 1n transverse vertical section taken on ie the irregular line 15 15 of Fig. 8;

ing devicewith some parts broken away and sectioned; :4

Fig. 18 is a front end tractor. with someparts removed and. further tion; m

a fragmentary ,view'partly in side elevation and partly in transverse vertical sec-' tion taken on the line 19-19 of Fig. 18

Fig. 20 is a view partly in plan andpartly .in transversehorizontal sectiontaken 0n the 1ine20.2O of Fig. 3, on an enlarged scale;

. Fig. 21 is a view partly in front. end eleva elevation of the trench an endless drivenbelt or chain27on which is mounted excavating buckets 28. This boom 26 is raised or lowered by a Windlass drum 29 and a cable 30 which runs over guide sheaves 31 on the frame of the trenching machine 25 and the boom 26. Any suitable transmission mechanism, not shown, may be provided for operating the Windlass drum 29; When the trenching machine 25 is in operation, the boom 26 is held in a downwardly and outwardly inclined position, as shown'in Fig. 1, and the depth of the trench A, may be varied, at will, by changing. the inclination of the boom to lower or raise the'free or lower end thereof to cause the buckets 28 to dig to the desired depth.

While in the drawings there is illustrated a given type of trenching machine, it'is of course understood that a steam shovel or any other suitable excavating method may be employed in digging the trench A. i

The trench tractor includes a rectangular main frame comprising a pair of laterally spaced side members, each of which includes upper, lower and intermediate longitudinally extended channel bars 32 and front, rear and intermediate upright channel bars or columns 33. These two main frame side members are rigidly connected by crosstie members 34, see Fig. [1, certain of which connect the two bottom bars at their lower flanges, and other of which connect the two front columns 33 together and the two rear columns 33- together. The flanges of the bars 32 are turned outwardand the flanges of the columns 33 are turned inward with the webs of said bars 32 and columns 33 contacting and rigidly connccted by rivets or otherwise I The intermediate columns 33 are located close to the front columns 33 and which front columns extend slightly above the top bars 32 and are rigidly connected by a top crosstie member 35. The rear columns 33 extend materially above the top bars 32 and are; rigidly connected by a' top cross tie member 36. As best shown inFig. 8,the bars 32 are extended rearward of the rear columns 33 and are progressively longer from the bottom up so that the rear end of the main frame is upwardly and rearwardly inclined. It isimportant to note that the top and bottom bars 33 are "vertically and horizontally spaced from theintermediate bar 32 to afford 'therebetween upper and lower ways 37 which extend horiillustrated a I zontal plane.

zontally between the intermediate and rear columns 33.

The trench tractor is designed to travel on the bottom of the trench as the same is dug by the trenching; machine 25 and, as shown, is

mounted on a traction device in the form of an endless tread belt 38. This tread belt 38 is arranged to run on the bottom of the trench A and is made up of a multiplicity of hingedly connected tread links or plates arranged to run over driven rear sprocket wheels 39, idle front sprocket wheels 40, and intermediate idle wheels 41. The shafts for the wheels 39, 40 and 41 are journaled in a pair of longitudinally extended sills 42 on which the side members of the main frame rests and are rigidly secured.

The tread belt 38 is driven from an internal. combustion engine mounted on the top of the main frame near the front end thereof and indicated as an entirety by the numeral 43 with the exception of a relatively small pulley 44- on the shaft of said engine. The driving connections from the engine 43 to the shaft of the driven sprocketwheels 39 include a belt 45 arranged to run over the pulley 44 and a relatively large pulley 46 on a countershaft 47 journaled in bearings on-the rear columns 33 above the top bar 32, a spur pinion 48 on the counter-shaft 47 which meshes witha large gear 49 on a driven shaft 'O'journa-led in bearings on the rearwardly projecting ends of the top bars 32 and a sprocket chain 51 which runs over a relatively small sprocket wheel 52 onthe driven shaft 501 and a relatively large sprocket wheel 53 on the shaft of the rear sprocket wheels39'. I

he trench tractor further includes trench wall retaining devices which, as shown, are in, the form of traction belts 54 arranged to contact with and travel longitudinally on the walls of the trench A and prevent the same from caving in, and at the same time afford auxiliary traction device which in the present arrangement of the trench tractor cooperates with the traction belt 38 in propolling the tractor. It is considered broadly new regardless of the character of the supporting and driving members of a trench tractor to provide the same with traction side belts. There is an upper pair and a lower pair of these traction belts 54, each of said pairs being mounted to travel in a hori- Normally the faces of each pair of belts 54 are substantially flush with theouter faces of the side members of the main frame for projecting movement into contact-with opposite walls of the trench A by pressure devices as will presently appear.

Each belt 54 is mounted in a supplemental frame 55, which, in turn is mounted in one of the ways 37 for horizontal sliding movement transversely of the main frame. The Ways 37 hold the supplemental frame 55 54 and assist in driving and guiding saidagainstmovement both vertically and longitudinally of the main frame. Each supple-' mental frame 55 comprises 'a pair of-vertically 'spaced horizontal plates '56 which 'ex- 5 belts are made longer than the upperbelts and extended rearward thereof, see .Fig. ,8. The two driven: sprocket wheels 59.:for the upperb'elts54 are secured tovertical shafts,

tend longitudinally in the respective way 37 and which plates are rigidly connected at their endsnear their outer longitudinal edges by a pair ofupright channel bars 57 the flanges of which a-reiturned inward; Said pairs ofplates 56 are also rigidly'connected at their'innerlongitudinal edges by a pair of upright angle bars 58. These-angle bars 58 further rigidly connect the upper and lower supplemental frames 54'on each sideof the main frame. The two angle bars 58 connectingthe upper andlower supplemental frames 55 on one side of the main frame have I the supplemental frames-55 against endwise movement longitudinally of themain frame and inrespect'to each other, but at the same timepermit lateral'movement of the connected supplemental frames 55 in respect to each other.

Each belt 54 comprises a plurality of hingedly connected plates or links set vertically 'endwise and mounted on a pair of driven rear sprocket wheels 59 and a pair of idle sprocket wheels "60. These pairs of sprocket wheels 59 and 60 cooperate with long upright internal teeth 61 on the backs of the belts 54 to guide and drive the same.

The sprocket wheels 59 and 60 have hex-- agon'al peripheries, in the corners of which are segmental seats arranged to receive the hinge oints between the links of the belts movement on the sprocket wheels 59 and 60 there isformed on'said belts upper and lower endless sectional tracks'62 which travel in circumferentially extended grooves 63 in the peripheries of said wheels and supports the belts 54'from the sprocket wheels 59and 60.

The belts 54 between the sprocket wheels '59 and 60 are held and'guided for straight line travel by uppera-nd lower idle wheels 64 which are mounted within} said belts. The sectional tracks 62 'travel-between the idle wheels 64 of the upper and lower pairs for contact With theopposing faces thereof to support and guide said belts. Upper and lower pairs of interr'ial' lugs-65 on the belts 54'are arranged toengage the outer faces of the wheels 64' and further hold'and guide said belts. By reference t-o'Fig. 12 it will be noted that; the idle wheels 64 and; the lugs 65 are reversely beveled to direct said lugs'onto the-wheelsduring the travelof the belts 54. I 1 in order to independently drive either the upper "or lower pair ofbelts 54, said lower 66 j'ournaled on the upper supplemental frames 55,and the sprocket wheels 59 for the lower belts 54 are secured to vertical shafts 1 Steps of traveling movement are imparted to the belts 54 from the driven shaft 50 by ratchet wheels 69 onthe upper ends of the shafts 66 and 67, and cooperating pawls 70 pivoted to a pawl reciprocating device in the form of a longitudinally extended horizontal bar 71. This-bar 71 is mounted between pairs of front and rear guide rollers 72 journaled in bearings 73 on the upper bars 32 and...

held retracted by a coiled spring 74. This spring 74 is compressed between a spring seat 7 5, on the front end of the bar 71, and a spring seat76 on an abutment 77 rigidly secured to a'crosstie member 78 connecting the top bars 32. The pawls 70am arranged in front and rear pairs with the former extending between the ratchet wheels. 69 on the shafts 66 for cooperation therewith to rotate said shafts and impartsteps'of movement to the upper pair of belts 54. Said rear pairof 'p'awls 7 O extend between the ratchet wheels 69 on the shaft'67 for cooperation therewith to rotate said shafts and impart steps of movement to the lower pair of belts 54. The 1;;

pawls 7 O of each pair areoutwardly and'reversely extended and. are yieldingly held in contact with the respective pair of ratchet Wheels 69 by a coiled spring 79 compressed between said pawls and mounted in seats on j;

the backs thereof, as best shown in F ig'. 13. 'Toi render either pair of pawls 7 Oinactijve so that the respective belts M will remain idle, said pawls are provided with rear extensions 80 between which extends a cam head'- f ll 81 secured toa short shaft 82 journaled in the bar 73 and an overlyingbridge bar. 88 secured thereto. On the upper end of the shaft 82 is a hand'lever 84 by which said. shaft may I clearance between the pawl extensions 80 and cam heads 81 when the pawls 70 are active to permit free movement of said'pawls' over the teeth of the ratchet wheels 69. By giving 1;.

the levers 84 a one-quarter turnythe cam 7 heads 81 Wlll'bB'IIlQVQCl into engagement with the pawl extensions 80 and therebymove the pawl's ;70vof each pair toward each other against thetension of the springs 7 9 and out I 30 with the sections thereof held in cylindrical of contact withthe teeth of the ratchet wheels 69. I To render any one of the pawls 70 inactive so that the respective belt 54 will remain idle, there is mounted in the reciprocating bar .71, at each pawl extension 80,'aremov-, able lock pin 85.

These look pins 85 are arranged to beplaced back of the pawl extensions 80 to hold the pawls70 inactive, as one thereofis indicated by broken lines in Fig. 13.

To operate the pawl carrier 71 and thereby cause the pawls 70 to impart steps of movement to the ratchet wheels 69, which, in turn, rotate the shafts .66 and 67; and operate the belts 54, as previously described, there is formed on each side of the gear 49 a plurality of circumferentially spaced peripheral cams 86 which engage a pair of cam rollers 87 on the rear end ofthe pawl carrier 71 and which rollers are yieldingly held by the coiled spring 7 4, in contact with said cams.

The belts 54 of each pair are yieldingly pressed against the walls of the trench A by a pair of coiled springs 88 for independent movement to produce: the necessary traction I to move the trench tractor and compensate.

for varying widthsin the trench A, unevenness of the walls thereof and inwardly projecting stones, roots, or other ob ects in sa d walls. Each spring .88 is formed in two parts casings 89 secured to the backs ofthe supple Inental frame bars 57 and'against the inner faces of which bars the outer end of sa d spring sections engage.

An adjustable abutment 90 is interposed 7 between'thesections ofeach spring 88 and comprises right andleft-hand screw rods 91 connected by a nut-acting member 92. The outer end portions of the screw rods 91 extend through apertures in the closed inner ends of the casings 89 from which the abutments 90 are supported. Said screw rods 91 are held from turning with the nut-acting members 92 bykeys on the closed ends of the casing 89 and which keys extend. into longitudinally extended keyeways in said rods to permit longitudinal movement of said rods. The

' nut-acting member on the screw rods 91 to which it is applied.

To operate the lower pair of abutments 90,

. sprocket chains 95 run over sprocket wheels 7 96 on the upper nut-acting members 92 and sprocket wheels 97 on the underlying nutacting members 92. If desired or found necessary, the two lower abutments 92 may be adjusted by operating the upper pair of .nut-acting'members 92 and then the chains 95 removed and the upper pair of nut-acting members92 operated'to adjust the two upper abutments 92.

i .It may be here stated, that there is sufficient clearance in the ways 37 for the belts 54 and supplemental frames 55 to permit free movements thereof transversely of its main frame or slight angular movements in retrench A under the desired pressure. If desired, more tension may be placed on the springs 88 at the rear ends of the belts 54 so that said belts will more easily travel longitudinally on the side walls of the'trench A, or greater pressure may be applied to either the upper or lower pair of belts 54 to better hold the side walls of the trench A.

To level or smooth the bottom of the trench A in advance of the trench tractor, there is provided a scraper blade 98 hinged to the lower end of a front plate or shield 99 and which scraper blade is held in an inclined operativeposition in front of said tractor by a' pair of supporting rollers 100 on which said scraper blade rests, intermediate of its upper and'lower edges. This scraper blade 98 extends the full width of the main frame and the shield 99 completely closes the front end'of the main frame and is mounted in guide brackets 101 for raising and lowering movements. The supporting rollers 100 are j ournaled in the oblique front end portions of the lower bars 32 which are extended forward of the front columns 33.

' To raise and lower the scraper blade 98 and hold the same in an operative position,

as shown by full lines in Figs. 18 and 19,

or in anoperative position, as shown by broken linesin Fig. '19, there is provided anupright screw rod 102 having screw-threaded engagement with a bracket'103 on the back of the shield 99. This screw rod 102 is turnably mounted at its lower end in a step bearing 104 on the forwardly projecting ends of the lower bars 32 and its upper end is turnably mounted in a bearing 105 on the crosstie bar 35. A hand wheel 106 is journaled in the bearing 105 at the back of the shield 99 k to turn about a horizontal axis and is con nected, by a pair of intermeshing bevel gears 107, to the upperv end of the screw rod 102. Referring now in detail to the sheathing device, which is drawn in the trench A by .85 the belts 54 against the side walls of the the trench tractor, the samejincludes a pair of laterally spaced side membersflEa'ch of these side members Comprises an upwardly and rearwardly inclined channel bar 108, up-

per, lower and intermediate longitudinally extended channel bars 109 and a' side plate bottom of the trench A. The lower rod 113 tfe travel of thesheathing device thereon.

is extended outward ofvthe side plates 110 to afforda pair of trunnions journaled in bearings 116 in the webs of the rcarwardly projecting ends the lower bars 32, see Fig. 8, and connect the sheathing device to the trench tractor for movement therewith and with freedom for pivotal movement on SiLlCl trunnions, whereby the sheathing device is free for movement in avvert-ica'l plane about the axis of said trunnions.

It isimportant to notethat trench tractor on the sheathing device, which keeps the same with its shoe 114 resting on the bottom of the trench A and overcomes any tendency thereof to work up in the trench A by its frictional contactwith the side Walls of said trench and out of contact with the bottom thereof. I r

.The sheathing device is of substantially "3 the same width and height as the trenchtrae- 1 tor, and the crosstie bars111 are-s0 arranged as not to interfere with the workmen ithin said device. Theshoe 114 also affords a plat form on which the workmen maystand While :6; working in the trench, and byreference. to

Fig. 16', it will be noted that-said shoeterminates materially short of the rear end, of the sheathing device so that apipeor pipe sections may be laid or built withinthe sheathing device.

It will also be-bnoted by Figs..8 and 16,

that the side plates.f110,at thefrontofthein lowerlongitudinal edges, and the front portion of the shoe 114 are upwardly" and for-. wardly inclined so that the sheathing device may be turned on its trunnions 116..without coming in contact with the bottom. of the trench A. This'upwardly inclinedfront pork: tion of the shoe 114 also causes the shoe to ride over the bottom of the trench during the To raise or lower the sheathing device by turning the same on itstrunnion 115and to hold the same raised with its shoe 114 above 7 the ground so that the sheathing device may the trunnions 115 connect the sheathing device to the trench tractor only slightly above the tread, traction. belt 38 so that there is a direct pull by the be easily. carried by the trench tractor when movingfrom'place to place, there is provided I a cable 117, one end of which is attached to the crosstie rod 112 and its other end is ar ranged to be wound on a Windlass drum 1'18 jonrnaledon the rear columns 33 at the tops thereof. r For operating the Windlass drum 118,

thereis secured to one end of its shaft a worm gear 119 which meshes with a worm 120,the shaft of which is journ'aled in bearings'on' the crosstie bar 36. A hand Wheel I 121is'applied to the inner end of the shaft of theworm'120 for rotating said worm and I hence the Windlass drum 118'. 'Obviously,

the Worm gear 119 and Worm 120 afford a lock to prevent rotation-of the Windlass drum 118 under the pulling action on the cable by the raised sheathing device. Pairs'of front and rear wheels 122 and 123, respectively, are provided to be removably applied to'th'e trench tractor'whenfout of; the trench A to assist in: transporting the same from'place to place and to hold the same in an upright position and prevent tipping. Said pair .of'front Wheels 122 are journaled on spindles 124attachedby steeringlmuckles 125 to stub axles 126; These axles 126 are square in crosssection and removably telescop'ed mto'the' ends of a square box 127, as-best shown in Figs. 20' and .21;

This box 127 extends transversely ofthe main frame, rests onthe top flange of its lower bars 32, and is rigidly secured'thereto, The axles 126 are rigidly but detachably secured the box 127 by n.utequipped bolts 128.

' The two spindles'124 are connectedfor common steering movement by a pairgof fixed arms 129 'on said spindles and a crosstie rod'130, the ends of which a-repivotally connected to said arms at their outer ends. Angular steering movement is imparted to 122 by a hand wheel 131 on the upper end of a steering post 132, the lower endof which is turnably mounted in upper and lower bear ings 133 formed With the respective 1 stub,

axle126 andhavinga cam head 134 which works in a cam slot 135 in an extension/on said-spindle. "A platform 136' is secured to the stub axle 126 having the bearings 133 and on which platform the operator stands when operating the steering Wheel 131-to guide the'trench tractor.

The rear Wheels 123 are journaleddirectly 3 on stub axles of thesame type as those shown, in Figs. 20 and 21, and which axles are remov ably mounted in a rear box 137 of the same type as the box 127 and secured to the main frame in the same manner.

detachablysecured in the box 137 by nutequipped bolts, not shown.

The diameters of the front and rear wheels 122 and 123, respectively, are such'that the The stub axles 1 for the rear wheels 123 may be rigidly but one of the spindles 124 and hence the wheels front end of the trenchtractor is supported on the front wheels 122 and the forward end portion of the tread traction belt 38 is lifted slightly from the ground and the rear end portion thereof is in contact with the ground to afford the necessary traction for moving the tractor.

The trench tractor may be made in various different widths and heights to travel in trenches of given widths and depths depending on the kind of service pipes to be laid therein.

\Vhen it is necessary to dig a trench that is deeper than the height of v the; trench tractor and sheathing device, in

order to secure the proper grade for the pipe being-laid therein, supplemental trench wallretaining members 137' and 138 are mounted on the tops of the side members of said tractor and sheathing device, respectively, to form extensions thereof. These suppleme-ntal members 137 and 138 are rigidly but de tachably securedto the res'pectiveside members of the trench tractor and sheathing device bynut-equipped' bolts 139", as shown in Fig. 7. Said two. supplemental members 137 and the'two supplemental members 138 are connected and held laterally spaced by cross tiemembers 140, as shown Fig.6.

The operation of the trench tractor may be briefly described as follows:

,The trenchingv machine 25, in digging the trench A,'forms the ends'of said trench on inclines so that the trench tractor may enter I andleave said trench by its own power. The J trench tractor is propelled from one job to the other and in the trench A on its tread.

belt 38' which is. driven'froni the engine 43. As previously stated, the .trenclrtractor is moved to a job with'the front wheels 122' and rear wheels 123 attached thcreto,'as pre viously described. v I

Just before the trench tractor enters. the trench A, on the inclined front end thereof, the front wheels 122 are removed and the 5 windlass drum 1'18 operated to lower the rear end of thesheathing' device and allow. the same to be supported on thegronnd' by itsshoe 11 1. By relieving the trench tractor from the weight of'the sheathing device thereon WlllCll t'euds'to lift the front end of the trench tractor by the pull of its cable 117 on the inclined front" end of the trench A, the rear wheels 1523 are removed. 'To remove the front Wheels 122 the front end ofthe tread belt 38 may be moved onto a block of wood or other obstruction to lift said wheels from the groundor holes may be dug undersaid' wheels to release the same from the weight of the tractor.

The rear wheels 123 may be readily applied or removed from the trench tractor forthe reason thatthey are usually out of contact Qwithithe ground. I

Except when thetren'ch tractor is operatingfin the trench A, thepawls are inactive by the cam heads 81 so that the belts 54 are idle. hen the tractor is going into the trenchA or out of thesame, the idle belts 54 will engage the side walls of said trench and be moved thereby which materially reduces the friction between the tractor and side walls of the trench A so that said tractor will enter the trench with comparatively little effort. v I

After the trenchtractor is in the'trench A the springs 88 are placed under the desired tension to press the belts 5 1- against the walls of said trench and then the levers are operated to release the pawls 70, and permit the same to engage the ratchet wheel 69', under the reciprocatory movement of the pawl carrier 73, and impart relatively quick steps of movement to said belts to produce surfacetravel thereto at the samerspeed as that of the tread belt 38.

These belts 54, with the assistance of the main frame of the trench tractor, support the walls of the trench A as they are dug by the trenching device and prevent the same from caving in Said "bolts 54: also perform another important function in that they afford auxiliary traction which materially assists' the tread belt 38in moving the tractor in the trench A and overcome any tendency thereoftowork up on the side walls of the trench. I

By manipulating the levers 84:, the driving means for either the upper pair of lower pair of belts 54 may be cut out 'of action while the other is being operated, to facilitate the -handling of the tractor. By the use of the'sto'p 'pins 85, any one of the pawls 70 may. be rendered inactive so that the driving means'for the-respective belt'54l will remain idle. It w'ill thus be seenthiat either one of the upper orlower belts may be dri ven'while the other thereof is, not.

The sheathing device is of a" width slightly less than that of the main 'frameof the tread tractor and with its frontend extending between the oblique rear ends of the mainframe side nembers so that said device will be drawn through the trench A by the tractor with comparatively little effort and by the direct pulllthereon'from the tractor will always remainon' the bottom of the trench A. The termination of the" shoe 1'14 considerably forward from therear end of the sheathing device {permits the laying of a pipe within the device so that the workmen and work are alwaysfully protected by the sheathing device. y V

At the:complet-ion'ofthelaying of the pipe B'in thetreiich A andibefore thetrench tractor is moved out of said trenclnthe Windlass drum118'is operated to lift the rear end or so i I the sheathing device by means of the cable 117 and support the same entirely from the tractor. This lifting of the sheathing clevice by the cable 117 produces a rearward pull on the upper ends of the columns-33 which tends to lift the forward end of the trench tractor to cause the same to travel more easily up the inclined rear end of said trench. While the tractor is still on the inclined rear end of the trench A with its front end projecting above the surface of the ground, the front. wheels 122 are applied thereto without the use of a jack, and after said tractor is entirely out of the trench A, the rear wheels are applied thereto.

VVhatIclaim isz I 1. A trench tractor adapted to travel longitudinally on the bottom ofa trench having trench side wall retaining devices capable of surface travel longitudinally on the side walls of the trench equal to that of the tractor. I 2. The structure defined in claim 1 in further combination withpower means carried by the tractor for driving said devices.

3. A trench tractor adapted to travel longitudin ally on the bottom of a trench having a pair of-trench side wall retaining endless belts capable of surface travel longitudinally on the side wallsof a trench equal to that of the tractor. I v

4. A trench tractoradapted to travel longitudinally on the bottom of a trench having a pair of trench side wall retaining traction belts arranged to travel longitudinally on the side walls of the trench, and power means carried by the tractor for driving the belts.

5. A trench tractor adapted to travel l-ongitudinally onthe bottom'of a trench having a pair of trench side wall retaining traction belts arranged tov travel longitudinally on the side walls of thetrench, and'power means operative at will for driving either one or both'of the belts. g 6. A trench tractor having anupper pair and a lower pair of trench wall retaining traction belts, and power means for driving the belts.

7. A trench tractor and power means for independently driving ther combination with means for adjusting the pressure devices to render the same in-,

active.

11. A trenchtractor, trench side wallretaining traction belts, power means for driving the belts,.front and rear pressure devices for holding the belts against the side walls of a trench, and means for independently adjusting the pressure devices to vary'the independentlyholding the belts of either pair against the side walls of a. trench.

13. Atrench tractor having amain frame,

a pair of supplemental frames mounted on the main framefor independent movement transversely thereof, a trench side wall retaming traction belt mounted on each supplemental frame, yielding pressure devices for holding the belts against the side walls of the trench, and power means for driving the belts.

14. A trench tractor having a main frame,

an upper pair and a lower pair of supple- 'mental frames mounted on the main frame,

the supplemental frames of each pair having independent movement tranSVersely f the main frame, a trench side wall retaining traction belt mounted in each supplemental frame,.front and rear yielding'pressure devices for holding the belts of each pair of supplemental frames against the'side walls of a trench, and power means for independently driving the belts of each pair.-

In testimony whereof I afiix mysignature.

GEORGE H. GRE-IMAN.

either the upper or lower pair of belts or f both pairs of belts. g

i 8. A trench tractor having an upper pair and a lower pair oftrench wall retaining belts, and power means for independently driving both pairs of belts or either the upper or lower pair of belts or any one of the belts or both pairs.

9. A trench tractor, trench. side wall retaining traction belts, power means for driv-' ing the belts, and yielding pressure devices for holding the belts against the side walls of a trench.

10. The structure defined in claim 9 in fur:

ice 

